Line Pipe Welded Zone Cooling for Low-Temperature Toughness
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Solution Overview
Problem
Existing steel pipes for line pipes face challenges in achieving high-strength and low-temperature toughness, particularly in the welded zones, leading to potential brittle fractures, with a lack of effective cooling systems to enhance toughness.
Innovation Solution
A method involving controlled alloy composition and high-frequency heat-treatment followed by precise cooling processes, including rapid, air, and water-cooling, to create a microstructure with spherical carbides and fine ferrites, enhancing the welded zone's toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-strength steel sheet is used to increase transport pressure and capacity, then transport efficiency is improved, but low temperature toughness of welded zone deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling alloying element compositions (C: 0.02-0.07%, Si: 0.10-1.00%, Mn: 1.00-2.00%, etc.) and implementing a multi-stage heat treatment process with specific temperature ranges and cooling rates to achieve both high strength and improved low-temperature toughness in the welded zone
Solution Approach 2:
The patent applies local quality by performing selective heat treatment only on the welded zone rather than the entire pipe, and by creating a specific microstructure (spherical carbides and fine ferrite) localized in the welded area to improve toughness without affecting the overall high-strength properties of the pipe
2Reliability
If conventional heat-treatment technology is applied to welded zone, then low temperature toughness is partially improved, but shock absorption energy remains insufficient
Solution Approach 1:
The patent segments the cooling process into three distinct stages with different cooling rates and target temperatures: rapid cooling to 550-710°C, air cooling to 300-400°C, and water cooling to room temperature. This segmented approach creates the desired complex microstructure with spherical carbides and fine ferrite that achieves both toughness and shock absorption energy
Solution Approach 2:
The patent applies dynamics by using dynamic cooling rates that change through the process - initially rapid cooling to suppress unwanted phases, then slower air cooling to allow fine ferrite formation, and finally water cooling to complete the transformation. This dynamic control of cooling rate optimizes the microstructure for both toughness and shock absorption
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method results in a steel pipe with improved low-temperature toughness, achieving a shock absorption energy value of 27J or greater at -45°C, suitable for pipelines and offshore structures.
Implementation Method 1
performing high frequency heat-treatment of the welded zone of the steel pipe for the line pipe
Implementation Method 2
rapidly-cooling the high frequency heat-treated welded zone to 550 to 710° C.
Implementation Method 3
air-cooling the rapidly-cooled welded zone to 300 to 400° C.
Implementation Method 4
water-cooling the air-cooled welded zone
Implementation Method 5
welding the welded zone in an electric resistance welding scheme
Data Source
AI summary
Disclosed are a steel pipe for a line pipe having excellent low temperature toughness in a welded zone thereof, and a method for manufacturing the same, in which alloy components and a ratio thereof are controlled, and high frequency heat-treatment is carried out on the welded zone, and immediately thereafter, a cooling process is performed thereon in a strictly controlled manner, thereby improving the low temperature toughness of the welded zone, such that a resulting steel pipe is suitable for use in a pipeline and an offshore structure.